In my single-player, Hard campaign game - I've found that Metsuke (the secret police of Shogun 2) agents are useful to boost income and catch enemy ninja. What confuses me is why I can't hire any more - the tool-tip indicates that it is based on the number of market-chain buildings I have, and I am sure I have more markets than Metsuke.

Also, it is not clear whether an upgrade to a market counts as an extra 'market-chain' building - I am guessing that it doesn't.

From browsing forums, it seem there is a hard-limit of 5 agents of any type, regardless of how many chains you have. You can never have more than 5 Metsuke, 5 Ninjas, 5 Monks, etc. forums.totalwar.org/vb/…
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JonathanJApr 11 '11 at 3:21